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Uncle Phil
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Documentation Of Proper Fuel Pressure For ST1100
- Thread starter Uncle Phil
- Start date
Uncle Phil :
I used a plain old auto standard metal 5/16 " fuel filter with barbs on each end and got the check valve from McMaster-Carr. The fuel filter easily fits inside the gas tank right above the fuel pump. It took a few tries futzing with the right combination of brass fittings to get the check valve in the correct position below where the cut-off valve used to be.
You may have seen this pic before ( before I installed the fuel filter )
I used a plain old auto standard metal 5/16 " fuel filter with barbs on each end and got the check valve from McMaster-Carr. The fuel filter easily fits inside the gas tank right above the fuel pump. It took a few tries futzing with the right combination of brass fittings to get the check valve in the correct position below where the cut-off valve used to be.
You may have seen this pic before ( before I installed the fuel filter )
Heh, that is such a distant memory now. The ST pump is the lowest pressure pump I have ever encountered. At the time, there really wasn't anything available for aftermarket that low.
The Oz/inches units are directly from a low pressure gauge used. It's not a gauge you find standard since it's such low pressure.
'Ceptin' gravity, of course.
How low could one get fuel from the tank on an 1100 with gravity alone (presuming nothing restrictive in the pathway)?
I guess what I'm actually asking is: what is the relative height between the tank and the carbs?
The lower part of the ST1100 tank winds up below the carbs. I get your point, there would have been no need for a pump otherwise. The issue always occurred when the fuel tank was low. I assumed it was because the fuel would heat up as the level got lower. But it could be that the pump was already locked up and gravity no longer was our friend.
rwthomas1
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I'm wondering if a small "hopper" installed in place of the fuel petcock thingie would do it. Say 6-8oz in volume, a low inlet, and a low outlet, then a single outlet at the highest point, routing back to the tank.
The idea is the pump would fill this "hopper" and fuel would gravity drain to the carbs from the low outlet. The hopper would fill, and any excess would run out the outlet at the top of the unit, and back to the tank.
This would be a very simple device, allowing gravity to flow to the carbs, yet not really pressurize them. No moving parts and nothing to fail or wear out.
A pump running a setup like that would have an easy life.
RT
The idea is the pump would fill this "hopper" and fuel would gravity drain to the carbs from the low outlet. The hopper would fill, and any excess would run out the outlet at the top of the unit, and back to the tank.
This would be a very simple device, allowing gravity to flow to the carbs, yet not really pressurize them. No moving parts and nothing to fail or wear out.
A pump running a setup like that would have an easy life.
RT
An Artesian well of sorts. I like it. 
Just thinking, why wouldn't a pair of simple tees work as well? Add a tee to the output of the pump that circulates to the line ahead of the pump.
Just thinking, why wouldn't a pair of simple tees work as well? Add a tee to the output of the pump that circulates to the line ahead of the pump.
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Uncle Phil
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Got the McMaster-Carr number by any chance?
rwthomas1
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Hello Larry,An Artesian well of sorts. I like it.
Just thinking, why wouldn't a pair of simple tees work as well? Add a tee to the output of the pump that circulates to the line ahead of the pump.
Actually right after I posted I thought of that. Output from the pump to a T, about where the factory petcock is. The "straight through" to the carbs, and the branch back to the tank.
Two possible refinements: If fuel flow proved to be inadequate, a restrictor could be placed in the return line.
Also, if the return line was ABOVE the fuel level in the tank, it would act as a vacuum break, and the ability to run with no pump, and the tank half full, or higher, would be lost. The simple solution is to route that return to a low point in the tank.
Again, this solution should work with any higher volume/pressure than stock spec pump.
An elegant simple solution with no moving parts that will never wear out or break.
RT
Uncle Phil : Sorry, I don't but it was one of these : Check Valve for Fuel
Besides being able to get rid of the OEM cut-off valve, these also drop a little pressure, which I thought was desirable to reduce the flow a bit of the auto low pressure fuel pump. Plenty of flow with the check valve. At 70 mph, the ST1100 is only using about 3 oz. of gas per minute, if my calculation is correct ( and I double-checked, no pun intended).
Besides being able to get rid of the OEM cut-off valve, these also drop a little pressure, which I thought was desirable to reduce the flow a bit of the auto low pressure fuel pump. Plenty of flow with the check valve. At 70 mph, the ST1100 is only using about 3 oz. of gas per minute, if my calculation is correct ( and I double-checked, no pun intended).
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Uncle Phil
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Thanks.
I removed the cutoff valve from all of my ST1100s after the first one failed and never looked back - about 300,000+ miles ago.
I've got the fuel pressure regulator in hand but Holiday Laziness has overcome me and it's not installed yet ...
The orifice idea has some merit, but will not restrict pressure to the carbs, just the flow rate. Since it needs to be large enough to supply full throttle, it will be too large at low idle and the pressure could still overcome the carb floats and cause a rich condition. The return line is a better option, but an orifice might still be needed and getting the correct split might be difficult. The small gravity tank would need to be vented to the atmosphere to avoid the same pressure issues. The pressure regulator is probably the best solution if the proper pressure rated pump is not available.
Note that I am just a dumb farm boy with an engineering degree and enough knowledge of hydraulics to be dangerous.
Neal
Note that I am just a dumb farm boy with an engineering degree and enough knowledge of hydraulics to be dangerous.
Neal
These are low pressure in-tank automotive fuel pumps, like used on a 1986 Accord with a carburetor. The needle & seat on a ST1100 should be able to handle 4 psi . Same type of needle & seat that is used on the Honda Accord carb.
Here are the pump specs : Low Pressure Auto Fuel Pump ( 2-4 psi )
At full throttle you only need oz. / minute , not gallons / minute. These pumps are plenty good to satisfy a ST1100.
Here are the pump specs : Low Pressure Auto Fuel Pump ( 2-4 psi )
At full throttle you only need oz. / minute , not gallons / minute. These pumps are plenty good to satisfy a ST1100.
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rwthomas1
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Nice find! And it may be applicable, but how was it installed in the car? Was there an inline regulator, and of a return line? Yes, the carb may be able to handle the pressures, but can the pump deadhead? If it can, you might have a winner. Airtex is a major aftermarket supplier, and known to be reliable. If it can't deadhead, or had a regulator, can the factory Honda unit be had? Parts that are designed to work together save a lot of headache.
RT
No regulator required - not a high pressure F.I. pump, only a regulator and return line is required for a F.I. system. The pressure speced ( 2-4 psi ) for the pump in the link above is the dead head pressure.
A F.I. pump has a dead head ( speced ) pressure way above the F.I. fuel rail operating pressure, that's why a regulator and return line is required for F.I.
See the spec on this FI pump : FI pump specs
A F.I. pump has a dead head ( speced ) pressure way above the F.I. fuel rail operating pressure, that's why a regulator and return line is required for F.I.
See the spec on this FI pump : FI pump specs
rwthomas1
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Then that pump should be gold! Nice find!
RT
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Uncle Phil
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Well, since I installed the FleaBay Chinese fuel pressure regulator and set it to 1.5, all is well with the Quantum fuel pump.
I'll be taking a long run to RanchSToc with the bike in April which will give me some more confidence in the set up - or not!
I'll be taking a long run to RanchSToc with the bike in April which will give me some more confidence in the set up - or not!